Asymmetric catalysis is the most efficient method for the generation of products with high enantiomeric purity, as the asymmetry of the catalyst is multiplied many times over in the generation of the chiral product. These chiral products have found numerous applications as building bocks for single enantiomer pharmaceuticals as well as in some agrochemicals. The asymmetric catalysts employed can be enzymatic or synthetic in nature. The latter types of catalyst have much greater promise than the former due to much greater latitude of applicable reaction types. Synthetic asymmetric catalysts are usually composed of a metal reaction center surrounded by one or more organic ligands. The ligands usually are generated in high enantiomeric purity, and are the agents inducing the asymmetry. These ligands are in general difficult to make and therefore expensive. A notable exception are chiral phosphine-aminophosphine ligands which are readily prepared and air-stable, and have been described by Boaz, N. W. and Debenham, S. D., U.S. Pat. No. 6,590,115. The phosphine-aminophosphine compounds disclosed in U.S. Pat. No. 6,590,115 may be combined with catalytically-active metals to form complexes useful as catalysts in asymmetric hydrogenation processes. Compounds that may be obtained from such asymmetric hydrogenation processes are of great interest in the pharmaceutical industry and include, but are not limited to, amino acids, 2-substituted succinates, and 2-hydroxyesters having high enantiomeric purity.
U.S. Pat. No. 6,590,115 discloses the synthesis of phosphino-aminophosphines by a three-step process wherein    (1) a dialkylamine-phosphine compound is reacted with a carboxylic acid anhydride to obtain the corresponding phosphine-ester compound;    (2) the phosphine-ester compound is reacted with a primary amine to obtain a secondary amine-phosphine compound; and    (3) the secondary amine-phosphine compound is reacted with a disubstituted phosphine halide.The third step of the published synthesis of the phosphine-aminophosphine compounds involves the coupling of the precursor secondary amine-phosphine compound with a suitably substituted dialkyl, diaryl, or alkyl aryl phosphine halide. This method is limited by several factors. For example, there are only a limited number of chlorophosphines that are commercially available and the preparation of disubstituted phosphine halide is often arduous. In addition, coupling of the amine with the phosphine halide may be subject to severe steric constraints, which may limit the types of substituents that may be present on the nitrogen atom of the secondary amine-phosphine reactant and/or on the phosphorus atom of the disubstituted phosphine halide reactant.